Method for applying heat reactive coatings



Feb. 20, 1968 J. G. SVRCHEK METHOD FOR APPLYING HEAT REACTIVE COATINGSFiled Aug. 9, 1966 g 1 1 w w I NVENTOR. J' fieynk 6502 472216 UnitedStates Patent 6 Claims. (31. 11747) ABSTRACT OF THE DISCLUSURE Method ofcoating pipe comprising continuously rotating a preheated pipe about itsaxis while spraying a heat sensitive resinous coating composition on thepipes surface to coat the pipe, and heating the thus coated pipe at atemperature which will cure and immobilize the coating by rotating thecoated surface through a heating zone, the coating applied perrevolution or pass having a thickness not exceeding about 0.43 mil,continuing the sequence of spraying and heating until the surface iscoated to a thickness of at least about 4.5 mils, and thereafter coolingto cause the coating to become hardened, all as described hereinafter,

This is a continuation-in-part of copending patent application Ser. No.255,441, filed Feb. 1, 1963, and now abandoned.

The present invention relates to an improved method and apparatus forapplying reactive coatings to surfaces, and particularly to theapplication of protective coatings for pipe.

In summary, this invention is directed to a method of applying a liquidheat sensitive resinous coating composition to a pipe surface whichcomprises preheating the pipe to a temperature sufficient to promotesetting of the resinous components in said composition, rotating saidpipe about its axis, spraying a film of said composition of a thicknessnot in excess of about 0.43 mil onto a portion Ofthe periphery of saidpipe, heating the coated pipe while the coating is still liquid at atemperature sufficient to immobilize the coating thereon, butinsuflicient to set the coating into a completely hard form, continuingthe sequence of spraying and heating until the periphery of the pipe iscoated with a coating measuring at least about 44.5 mils in thickness,and thereafter cooling the coating to cause the coating to becomehardened.

In a preferred embodiment of this invention, I apply a heat reactivecoating composition including a butadienestyrene copolymer containingfrom 75 to 85% butadiene and 15 to 25% styrene and a volatile solvent toa pipe which comprises preheating said pipe to a temperature in therange from 250 to 450 F., rotating said pipe about its axis, spraying afilm of said composition not in excess of about 0.43 mil in thickness toa portion of said pipe, heating the coated pipe at its outer surface toa temperature of at least 250 F. but below the temperature at which thecoating carbonizes to thereby volatilize off the solvent and acceleratethe setting of the copolymer into a coating which is highly viscous, andcontinuing rotation of the pipe and spraying and heating of thecopolymer until a coating is built up measuring at least 5 mils inthickness.

In the drawings:

FIG. 1 is a side elevational view of the apparatus of the instantinvention.

FIG. 2 is a plan view of a typical apparatus.

Probably the most prevalent method for protecting pipe which is to beburied underground involves the application of hot coatings such as coaltar pitch, asphalt, or wax 3,359,922 Patented Feb. 20, 1968 to thesurface of the pipe prior to laying it in the ground. While thesecoatings are relatively inexpensive raw materials, a substantial amountof labor is involved in applying them to the pipe and then theprotection which they afford is not as great as would be desired. Thechemical and electrical properties of such coatings on pipe are notcompletely satisfactory, and corrosion of the pipe occurs withsufficient frequency that this method of pipe protection is still lessthan wholly satisfactory. Hot applied coatings are also liable to damageduring transport and to damage by backfill materials used on the jobsite. The coatings are also subject to damage by bending of the pipeprior to laying, and are subject to disbonding because of weatherextremes or soil stresses.

One of the best methods for applying a completely resistant coating topipe has been described in US. Patent No. 3,028,257. Said patentdescribes the application of heat reactive polymers to surfaces andinvolves spraying a heat reactive, partly polymerized copolymer with aflammable liquid diluent at a temperature above the flash point of thediluent to atomize the coating composition, whereupon the resultingspray is directed through an envelope of flame and heat directed at thesurface to be coated. While in this zone, the polymerization of thecopolymer continues at a rapid rate so that shortly after application tothe surface in the form of a continuous film, the copolymer iscompletely set to an infusible coating which is completely resistant toattack by chemicals, soil bacteria, and electrolytic corrosion.

The process of the aforementioned patent has been successfully appliedto miles of large diameter pipe at an overall cost comparable to thecost of hot applied coatingwrapping systems. It has now been found thatthe cost of application of the heat sensitive resins can be furtherreduced by the process of the present invention. These economies areeffected by increasing the efiiciency of application while retainingmost of the desirable properties in the finished coating. In the processof the previously mentioned patent, some of the resin was unavoidablylost by burning in passing through the envelope of flames and heat. Withthe new process, significant savings in material can be eliected sincethe spray pattern is applied without passing it through a flame zone.

An object of the present invention is to provide an improved method forthe application of heat sensitive, resinous coating compositions to pipesurfaces.

A further object of the invention is to provide a method for theapplication of heat reactive, thermosetting resins to pipe surfaces toefiect savings in the amount of resin applied, while still building up asatisfactorily thick coating.

A further object of the invention is to provide an apparatus for theapplication of heat reactive, thermosetting coatings in a rapid andetficient manner.

Another object of the invention is to provide a method for putting downmany chemically bonded coatings consecutively, with intermediate heattreatment, thereby reducing the possibility of defects in the overallcoating.

A further object of the invention is to provide an apparatus forapplying very thin multiple films of a heat reactive copolymer to thesurface of a pipe, and continuously setting the material on the pipeuntil a satisfactory thickness of the cured coating is built up.

The present invention can be employed with many different types andcombinations of thermosetting resinous compositions, provided they canbe put into a form in which they can be applied as a thin film onto thesurface of a pipe. Among the numerous resins which can be used are thephenolic condensation products, epoxy resins, urea-formaldehyde resinsand the like. A particularly preferred class of resins for use in thisprocess are the thermosetting polymers based on butadiene such as poly-'butadienes, epoxidized polybutadienes and butadienestyrene copolymerswhich contain from about 75 to 85 parts butadiene and from to parts (byweight) styrene.

Some attempts have been made in the past to apply the heat reactivebutadiene-styrene copolymers onto the surface of a metal by spraying,brushing, or the like followed by application of a flame to the coatingto complete the copolymerization reaction. Unless extremely carefullycontrolled, most of these attempts ended in the 7 production ofunsuccessful coatings largely because solvent was trapped within theresinous coating and upon setting of the resinous components, thesolvent formed blisters which rendered the coating unsatisfactory.

I believe that one of the principal reasons that such techniques havefailed lies in the attempt to put down too thick a coating in each pass.The butadiene-styrene copolymers are excellent heat insulators and it ispractically impossible to finish curing a coating of a few mils or so,with complete removal of solvent, in the times that have heretofore beenallotted. Furthermore, prior attempts may have been unsuccessful becausethe coating layers deposited subsequently did not bond properly to theunderlying layers, so that the multilayer coating was subject todelamination.

In accordance with the present invention, the coating thickness appliedat each pass (i.e., per revolution of the pipe being coated) isextremely small, and the other variables are so controlled that eachfilm of copolymer which has been applied to the surface of the pipe ispartly cured with complete elimination of the solvent before the nextthin film is applied, but the film remains receptive to the next appliedfilm. In the practice of the present invention, I have found that 0.43mil (0.00043 inch) is substantially the upper limit of thickness of thecoating which can be applied per pass (i.e., per revolution of the pipe)since my work has shown that a per pass thickness of 0.46 mil isinoperable. Usually the thickness of coating applied per pass wherepracticing this invention is less than about 0.1 mil. However, I havealso obtained excellent results with a thickness per pass (i.e., perrevolution) of about 0.21, 0.23, 0.26 0.34, and 0.41 mil. Per pass (perrevolution) thicknesses of about 0.46 mil and greater have givenunacceptable coatings (e.g., coatings containing many fragile bubblesand numerous pin holes); such thicknesses are inoperable. I have alsofound that the aforementioned sequence of spraying and heating therotating pipe should be continued until the periphery of said pipe iscoated with a coating measuring at least about 4-4.5 mils and preferablyat least about 5 mils in thickness because thinner coatings sometimesfail in service.

In accordance with the present invention, the pipe to be coated ispreheated to a temperature sufficient to promote setting of the resinouscomponents in the composition. In the case of the aforementionedbutadiene-styrene copolymers, the preheating range usually extends fromabout 250 to 550 F. This range will vary, of course, with the type ofcopolymer being applied. The pipe or other object to be coated iscontinuously rotated during the application of the thin resinous filmand usually moved axially as well. The amount of material being appliedto the pipe and the speed of rotation of the pipe are adjusted so thatthe resulting film does not exceed a thickness of substantially 0.43mil. The coated pipe, in its rotation, carries the still wet coating toa curing station with suflicient velocity so that the coating is stillwet when it is subjeced to the heat at the curing station. Someadditional polymerization undoubtedly occurs in transit from theapplicator station to the curing station because of the substantialtemperature to which the pipe has been preheated. However, this smalldegree of reaction is not harmful and is indeed beneficial since itinitiates the setting reaction which is brought close to completion inthe curing station.

At the curing station, sufficient heat is applied to the coated pipe totransform the thin film of the coating into a tacky, viscous semi-solidwhich is immobile on the pipe but still has not reached the point ofcomplete solidification. For the butadiene-styrene copolymers, thismeans heating the coating to a temperature of at least 250 F., andpreferably not in excess of about 500 F. At substantially highertemperatures, carbonization of the coating is likely to occur.

The heating of the thin film of coating in the manner described, bothfrom the heat retained in the pipe and the heat applied exteriorly issufiicient to completely volatilize any solvent present and leave acoating which still has reactive sites for bonding with subsequentlyapplied coatings. Then, as the pipe is continuously rotated, anadditional thin layer of resinous composition is applied, bonding itselfto the reactive sites, and the process is repeated until a coating of atleast several mils thickness (usually about 4-4.5, or 5 mils, or more)is built up on the pipe.

The butadiene-styrene copolymers containing about 75 to parts butadieneand 15 to 25 parts styrene can be prepared in a number of mannersincluding reaction of the monomers in the presence of sodium. Thecopolymers may contain hardness modifying agents such as maleic acid,fumaric acid, thioglycolic acid, thiosalicylic acid, mercaptophthalicacid, itaconic acid, mesaconic acid, citraconic acid, acrylic acid oresters thereof in small amounts. They may also contain small amounts ofalkylated phenols, or other promoters. The copolymers may also containmodifiers such as acrylic nitriles, alkyl acrylates, vinyl acetate,vinyl ketones, cinnamaldehyde, thiglycolic acid, and the like. Thecopolymers may contain bodying agents such as maleic anhydride.

Suitable solvents for the butadiene-styrene copolymers in theirincompletely polymerized form include alkanols such as 2-propanol andethanol, petroleum naphthas having a boiling range of about to 120 C.,straight run mineral spirits'having a boiling range of about 150 to 200C., or hydrocarbons such as butane, pentane, benzene, toluene, xylene,cyclohexane, butenes, pentenes, or the like, alone or in admixture.Generally, the solvent is added in sufiicient amount to provide aconsistency suitable for the type of application which is to be used. Asa general rule, for spraying purposes, the solvent will be present inamounts of about 50 to 150 parts by weight for every 100 parts by weightof the incompletely copolymerized solids.

The butadiene-styrene copolymers described above are commerciallyavailable drying oils sold under the trademark Buton. As described inUS. Patent No. 2,762,851, and others, the butadiene and styrene may becopolymerized in the presence of sodium in a reaction diluent such as analiphatic hydrocarbon at temperatures ranging from about 25 to C. Colorproperties may be improved by the addition to the diluent of analiphatic ether or polyether such as dioxane-1,4 in amounts of from 10to 45 parts per parts of the monomers.

The commercial product is a liquid-apparently a solution of polymericdrying oil in a hydrocarbon solventhaving a viscosity ranging broadlyfrom 0.5 to 20 poises at a 50% nonvolatile matter content. TheStaudinger molecular weight of the polymeric constituents varies fromabout 2000 to 1000 corresponding to an intrinsic viscosity of about 0.15to 0.4 or 0 .6.

A further description of the present invention will be made inconjunction with the attached sheet of drawings which illustrates, in asomewhat diagrammatic fashion, the method and apparatus of the presentinvention.

Reference numeral 10 indicates generally a pipe to be coated, the pipebeing rotated on its axis by means of a motor diagrammaticallyillustrated at reference numeral 11. A battery of spray guns 12 havingfeed lines 13 for introducing the resinous composition and lines 14 forintroducing compressed air to apply a spray 1 6 to the periphery of thepipe during its rotation. For purposes of safety, there should be asubstantial amount of atomizing air so that the concentration offlammable solvent never reaches the explosive limit, and the atomizingair provides a cooling effect on the spray to keep it below the ignitiontemperature. The pipe is preheated prior to the application of the spray16 to a temperature suflicient to promote setting of the particularresinous components which are present in the spray. The materialdeposited by the spray gun 12 is a continuous thin film measuring not inexces of about 0.43 mil in thickness. As the film forms on the exteriorof the pipe 10, the polymerization reaction commences by virtue of thepreheat which has been given to the pipe. Nevertheless, the applied thinfilm is still liquid by the time it reaches a curing station generallyidentified at reference numeral 17 in the drawings. Here, a source ofheat such as a battery of nozzles 18 issue flames 19 which play on thesurface of the Wet coating to eliminate completely the solvent presentand to advance the polymerization reaction further. As mentionedpreviously, the temperature to which the coating is raised in the curingstep should be at least 250 F. for the butadiene-styrene type copolymer,but below the temperature at which carbonization would occur. Suitableheat sources include burners utilizing oxy-acetylene, natural gas-air,propane-oxygen, and the like. Non-flaming heaters may also be used, butbetter physical properties are achieved in the coating when the filmsare exposed to a naked flame.

When the coated portion of the pipe leaves the zone of heat provided bythe curing station 17, the coating is immobile, but tacky and viscous,and completely devoid of solvent. It is then ready for anotherapplication of the liquid coating from the spray guns 12 or otherapplicator means. Successive applications of the thin film are thenpartially cured at" the curing station and the required coatingthickness. is built up progressively. After the coated pipe has movedaxially out of the curing station and applicator zone the coating setsto a completely solid, hard coat. If desired, the final setting may beaccelerated by quenching the coating in a water bath.

As evident from the foregoing, it is necessary to control the variousvariables in the process in order to secure the best results. The rateof rotation of the pipe 10 and the amount of material issuing from thespray gun 12 should be closely adjusted so that the material is appliedin the form of a thin film, but a substantially continuous one. Thevelocity of the periphery of the pipe can vary widely, with ranges ofabout 10 to 500 feet per minute being typical.

The ability to lay down very thin films of liquid heat sensitivematerial, and to build up a substantial coating thickness fromsuperimposing a large number of such films is at least partiallyattributable to the manner in which the film is heated. The spray isinitially deposited upon a heated pipe which initiates the completion ofthe polymerization in the thin, substantially continuous film. Then,when the film comes within the heated zone provided by the curingstation, the polymerization reaction or the setting reaction issubstantially accelerated, because the film is being heated from bothsides in this zone. Any solvent that has been trapped in the film tendsto migrate from the inside edge of the film to the outside because theheat is applied initially from the inside of the film. The solvent is,therefore, completely volatilized by the time the film has left thecuring station and the film is in condition to receive a new filmdeposit.

While the drawings illustrate the process as applied to the exteriorcoating of pipe, it should be recognized that the process may beemployed for the internal coating of large diameter pipes as well.

It should be evident that various modifications can be made to thedescribed embodiments without departing from the scope of the presentinvention.

As used herein, the term percent means percent by weight, unlessotherwise defined where used, and the term parts means parts by weight,unless otherwise defined where used. One mil is 0.001 inch.

This invention is further illustrated by the following examples whichare illustrative only and which do not limit the scope of the invention.

Example I The material to be sprayed was a liquid butadienestyrenedrying oil composition having the following physical properties:

Non-volatile copolymer content percent 51.7 Solvent-Solvesso (mixture ofxylenes and toluene) percent 34.1 Isopropyl alcohol do 10 .5 Pigment do3.6 Specific gravity of solution 0.957 Viscosity, No. 4 Ford cup, 75 Fseconds 134 A three inch pipe was preheated to a temperature of 350 F.before applying coating resin (i.e., the aforesaid butadiene-styrenedrying oil and rotated at the rate of about 200 rpm. (revolutions perminute) while applying the resin. The aforesaid composition was sprayedonto the pipe surface as a continuous film, the rate of resinapplication was such that the film deposited per revolution measuredless than 0.1 mil in thickness. A curing ing flame derived by thecombustion of acetylene was played on the surface of the pipe about 180from the spray station.

The coating was heated at the curing station to an estimated temperatureof 400 F. The thus coated pipe was cooled to ambient temperature (i.e.,ca. 75 F.). A coating build up of about 7 mils resulted; this coatingcured excellently and had a pencil hardness of 6H, i.e., it resistedpenetration by a 6H pencil, successfully resisted impact by a ball peenhammer and was free of bubbles and pin holes.

Example 11 The general procedure of Example I was repeated; however, inthis instance the pipe was preheated to a temperature of about 400 F.,and the rate of rotation was about 28 rpm. The rate of resin applicationwas such that a film having a thickness of about 0.21 mil was depositedper revolution. A coating build up of about 6 mils resulted. Thiscoating cured excellently; it successfully resisted impact by a ballpeen hammer, and it was free of bubbles and pin holes.

Example III The general procedure of Example II was repeated, but inthis instance the pipe was rotated at about 21 r.p.m. and the rate ofresin application was such that a film having a thickness of about 0.34mil was deposited per revolution. A coating build up of about 7 milsresulted. This coating cured excellently; it resisted impact by a ballpeen hammer and was free of bubbles and pin holes."

Example IV The general procedure of Example II was repeated, but in thisinstance the pipe was rotated at about 11 r.p.m. and the rate of resinapplication was such that a film having a thickness of about 0.41 milwas deposited per revolution. A coating buildup of about 4.5 milsresulted. This coating cured excellently; it resisted impact by a ballpeen hammer, and it was free of bubbles and pin holes.

Example V The general procedure of Example II was repeated, but in thisinstance the rate of resin application was such that a film having athickness of about 0.46 mil was deposited per revolution. A coatingbuild up of about 4.6 mils resulted. This coating had a frothyappearance; numerous bubbles were present in this coating which also hada large number of pin 'holes. Said coating was unacceptable,

thereby showing that a rate of application of resin which will deposit afilm thickness of 0.46 mil per revolution is inoperable.

Example VI The general procedure of Example II was repeated, but in thisinstance the pipe was rotated at about 6 /2 r.p.m. and the rate of resinapplication was such that a film having a thickness of about 0.9 mil wasdeposited per revolution. A coating build up of about 6 mils resulted.This coating was forthy in appearance and had hundreds of bubbles andpin holes. This coating was unacceptable.

What is claimed is:

1. The method of applying a liquid heat sensitive resinouscoating'composition to a pipe surface which comprises preheating thepipe to a temperature sufficient to promote setting of the resinouscomponents in said composition continuously rotating said pipe about itsaxis, spraying a film of said composition onto a portion of theperiphery of said pipe to coat the pipe, heating the thus coated pipewhile the coatingis still liquid at a temperature sufficient toimmobilize the coating thereon, but insuflicient to set the coating intoa completely hard form, said coating, as applied per pass, having athickness not in excess of about 0.43 mil, and continuing the sequenceof spraying and heating until the periphery of the pipe is coated with acoating measuring at least about 4.5 mils in thickness, and thereaftercooling the coating to cause the coating to become hardened.

2. The method of applying a heat reactive coating composition includinga butadiene-styrene copolymer containing from 75 to 85% butadiene .andto styrene and a volatile solvent to a pipe which comprises preheatingsaid pipe to a temperature in the range from 250 to 450 F., rotatingsaid pipe about its axis, spraying a film of said composition not inexcess of about 0.43 mil in thickness to a portion of said pipe, heatingthe coated pipe at its outer surface to a temperature of at least 250 F.but below the temperature at which the coating carbonizes to therebyvolatilize off the solvent and accelerate the setting of the copolymerinto a coating which is highly viscous, and continuing rotation of thepipe and spraying and heating of the copolymer until a coating is builtup measuring at least 5 mils in thickness.

3. The method of claim 1 in which said coating composition includes anincompletely polymerized butadienestyrene copolymer.

4. The method of claim 1 in which said coating composition includes anincompletely polymerized butadienestyrene copolymer and a volatilesolvent.

5. The method of claim 1 in which the coating measures at least about 5mils in thickness. 3

6. The process of claim 1 in which:

(a) the heat sensitive resinous coating composition is abutadiene-styrene copolymer containing from to parts butadiene and from15 to 25 parts styrene;

(b) the pipe is preheated to a temperature in the range from 250 to 550F.;

(c) the pipe is rotated about its axis with the velocity of theperiphery of the pipe being about 10 to 500 feet per minute;

((1) the coated pipe is heated to 250-500 F.; and

(e) the sequence of spraying and heating is continued until theperiphery of the pipe is coated with a coating measuring at least about5 mils in thickness.

References Cited UNITED STATES PATENTS 1,978,415 10/1934 Collins117105.4 X 2,963,045 12/1960 Canevari et al. 117-46 X 2,974,364 3/1961Lambert et al. 18-15 X 3,009,209 11/1961 Wein'brenner et al. 264309 X3,028,257 4/ 1962 Svrchek et al. 11746 3,108,022 10/1963 Church 117-18 XRALPH S. KENDALL, Primary Examiner.

ALFRED L. LEAVITT, Examiner.

E. B. LIPSCOMB III, Assistant Examiner.

